This invention relates to a method for the preparation of aromatic amines.
The benzenamines, also known as anilines and as aminobenzenes, are a known class of compounds having commercial utility as chemical intermediates, for a wide range of chemical end products. Substituted benzenamines, especially trifluoromethyl-substituted benzenamines are particularly useful as intermediates for the preparation of various dyestuff and pesticides. For example, 2-Amino-5-chlorobenzotrifluoride (also known as 4-chloro-2-(trifluoromethyl)benzenamine), is employed commercially as a dye intermediate and is designated as C. I. Azoic Diazo Component 17, according to Colour Index, Chemical No. 37055, Vol. 1-4, 2nd ed. 1956, Suppl. 1963 published by the Society of Dyers and Colourists (U.K.) and The American Association of Textile Chemists and Colorists (U.S.).
Substituted benzenamines, such as (trifluoromethyl)benzenamines are disclosed in U.S. Pat. No. 4,243,819 to Henrick et al., as intermediates in the synthesis of amino acid esters having pesticidal properties. Thus, for example, the reference teaches the preparation of such esters by reaction of various trifluoromethylanilines with m-phenoxybenzyl .alpha.-bromoisovalerate.
U.S. Pat. No. 4,316,988 to Clinton discloses the use of trifluoromethyl-substituted anilines as intermediates in the synthesis of various diphenylamine products useful as rodenticides, insecticides, and arachnicides.
The utility of benzenamines, including o-aminobenzotrifluorides as chemical intermediates has led to the investigation and development of various methods for the preparation of these compounds.
One known method for the preparation of aromatic amines, such as aniline, involves the reduction of an aromatic nitro compound. Thus, aniline may be prepared by reaction of nitrobenzene with hydrogen. McBee et al., J. Am. Chem. Soc. 73, 3932-34 (1951) disclose the preparation of 4-bromo-2-(trifluoromethyl)-aniline by nitration of 3-bromo-(trifluoromethyl)-benzene followed by reduction of the resultant 2-nitro-5-bromo(trifluoromethyl)-benzene.
U.S. Pat. No. 4,096,185 to Seiwell discloses the preparation of p-aminobenzotrifluoride (also known as 4-(trifluoromethyl)benzenamine) by reaction of p-chlorobenzotrifluoride with ammonia in a non-queous solvent in the presence of copper compound, such as cuprous chloride and a selected salt, such as potassium fluoride.
Forbes et al., Tetrahedron, Vol. 8, 67-72 (1960) prepared o-aminobenzotrifluoride by hydrogenation of 2-nitrotrifluoromethylbenzene at elevated temperatures and pressure in the presence of a Raney nickel catalyst.
German Offenlegungschrift D.E. No. 3,017,542 to Klauke et al. discloses the preparation of o-aminobenzotrifluoride by hydrogenation-hydrogenolysis of 2-amino-5-chlorobenzotrifluoride.
It is also known that isocyanates and carbamic acid fluorides are susceptible to hydrolysis, in a known manner, to form an amine. See Fieser and Fieser, Organic Chemistry, 3rd Ed D. C. Heath and Co. (1956). However, when the reaction is run neat, substantial quantities of urea may be formed as by-product. The formation of urea may be minimized, or avoided when a solvent, such as toluene, is employed, but the yields of amine are low.
Although methods for the preparation of aromatic amines, such as aminobenzotrifluorides are known from the prior art, it will be appreciated that the development of improved and more economical processes is desireable.
The present process differs substantially from the prior art process in the use of hydrogen fluoride and phenyl carbamic acid fluoride as reactants. The preparation of the phenyl carbamyl fluorides by reaction of phenyl isocyanates and hydrogen fluoride is known. Buckley et al. J. Chem. Soc. 864 (1945) disclose the preparation of phenyl carbamic acid fluorides by reaction of HF with various isocyanates. However, the reference provides no teaching relative to the fluorination of aromatic isocyanates bearing a haloalkyl side chain and no teaching or suggestion of the preparation of aromatic amines. The reference further discloses the treatment of phenylcarbamyl fluoride with water to result in the formation of diphenylurea.
British Pat. No. 955,898 (1964) to Farbenfabriken Bayer Aktiengesellschaft discloses the reaction of anhydrous hydrogen fluoride with chloromethylphenyl isocyanates to produce the corresponding fluoromethylphenyl carbamic acid fluoride, or, upon subsequent heating, the corresponding isocyanate. The British patent further discloses the reaction of hydrogen fluoride with 2-trichloromethyl-4-chlorophenyl isocyanate in chlorobenzene to prepare 2-trifluoromethyl-4-chlorophenyl carbamic acid fluoride. Subsequently, Klauke, Angew. Chem. Interat. Ed. Vol. 5, No. 9, 848, (1966), in contrast to the teachings of Brit. Pat. 955,898, stated that when o-trichloromethylphenyl isocyanate undergoes chlorine-fluorine exchange in anhydrous hydrogen fluoride; isomerization occurs simultaneously and o-N-(trifluoromethyl)aminobenzoyl fluoride can be isolated. In U.S. Pat. No. 3,829,460 to Buttner and Klauke assigned to Bayer Aktiengesellschaft, reference is made to the 1966 article and to earlier contradictory teachings and it is disclosed that when hydrogen fluoride is reacted with a trichloromethylphenyl isocyanate wherein the trichloromethyl group is in the 2-position to the isocyanate group, it is only possible to obtain the isomers, 2-N-trifluoromethylamino-benzoyl fluorides.
British Pat. No. 1,164,223 to Klauke et al. teaches the hydrolysis of trifluoromethylphenyl isocyanates with 90-100 percent sulfuric acid to produce the corresponding trifluoromethyl benzenamine (or amine.sulfate) with carbon dioxide as the only byproduct.
The hydrolysis of an NCO group with acid agent, such as concentrated hydrochloric acid or sulphamic acid is known (Houben-Weyl, Methoden der org. Chemie, 4th Edition, Vol. 11/1, page 953).
Although the utility and commercial value of aromatic amines has been generally recognized for many years; and, various investigations have been made of reactions of aromatic isocyanates, including aromatic isocyanates having a perchlorinated alkyl side chain, there has been no suggestion heretofore that aromatic amines can be prepared by the reaction of hydrogen fluoride with phenyl carbamic acid fluorides or their precursor phenyl isocyanates.